Programming

Question 1

What are functions used for?

Answer 1

Encapsulating code to do a particular job.
They create modularity
Promote good variable scoping and crearer control flow.

Question 2

What is an argument of a function?

Answer 2

The bit in brackets
‘def function(argument):’
A function can have many arguments

Question 3

What is the scope of a variable

Answer 3

The area of the code from which the variable can be used. Global variable have global scope (can be used anywhere), but function declared in a module can only be used in that module unless they are passed into another function as an argument.

Question 4

Unknown and unlimited arguments

Answer 4

‘*args’ is passed into a function as the argument to represent an unknown number of arguments.
‘**kwargs’ is passed into a function as the argument to represent key work arguments, e.g. “conf.xml”. These arguments are accessed by their key rather than position

Question 5

Pep8

Answer 5

PEP8 is a general style guide for commenting

Question 6

PEP257

Answer 6

PEP257 specifies docstrings that describe functions and modules

Question 7

RegEx characters

., ^, $, *, +, ?, []

Answer 7

. -Matches any characters except new line
^ -Matches the start of a string and immediately after new line
$ -Matches end of a string
* -Resulting RegEx matches 0 or more repetitions of given character(s)
+ -Resulting RegEx matches 1 or more repetitions of given character(s)
? -Resulting RegEx matches 0 or 1 repetition of given character(s) [not greedy]
[] -Used to indicate a set of characters in a set . E.g. [0-9A-Fa-f]

Question 8

Environment variables

Answer 8

import time
print(time.gmtime())
the gmtime bit is an environment variable

Question 9

Scripts - Inline direct execution

Answer 9

• Start to end execution
• Threads are created and managed per run or job
• The route through the program is largely predetermined and independent of other programs
• Idempotent programs – output should be reproducible (except for intentional randomness) with the same input

Question 10

Asynchronous execution

Answer 10

• Asynchronous jobs are run from a queue and don’t have to be executed in the order they occur
• Crucial for automation
• This can improve load management by reducing bottlenecks although can create concurrency issues

Question 11

Example of asynchronous event driven architecture

Answer 11

Websites use this

Flask

Question 12

Python Path

Answer 12

Environment variable where additional modules are stored - pip installs to here.

Question 13

Module used to schedule commands for a specific time

Answer 13

Sched module

Question 14

What is ‘@app.route(“/home”)’

Answer 14

Code for flsk to show code run when the /home page of your website is run

Question 15

Restful API calls

Answer 15

Using API key with a url to use data from a website in a program.
Data usually received in a .json file, and relevant parts can be taken from this.

Question 16

Software reliability - Defensive programming

Answer 16

Used for edge cases to stop program crashing

Question 17

Software reliability - Exceptions

Answer 17

An exception is raised when one one of these errors occurs:
IndexError I ValueError I EOFError I AssertionError I SyntaxError I
IndentationError I KeyboardInterrupt
or you can define your own exceptions

Question 18

Try-except (try-catch)

Answer 18

The try: … except: statement attempts to run code, but if it would raise an exception (crash the program), the code below except is executed instead

Question 19

try … except … finally

Answer 19

The try: … except: … finally: overrides all error handling as final block. The code under ‘finally’ will run regardless of any raised exceptions.

Question 20

‘raise’ keyword

Answer 20

To raise an exception in your code use the keyword raise - this is beneficial for defensive programming.

Question 21

Keyword for unit testing in python

Answer 21

'assert'
assert function(“test”) == “test result”

try:
tests()
except AssertionError as message:
print(message)
game_play()

assert “rat” in word_lookup(“tar”), “word_lookup: FAILED“

Question 22

Logging

Answer 22

• Log files keep a log of system activity
• Like a ledger they are immutable
• If something is created and then deleted the live system should have no record of it. However, the log should retain the update record
showing the existence of something for that period
- Logs record a persistent history of the system
• Log files have two main uses:
- Tracing errors; An error log
- Recording system events; A system log

Question 23

Slicing a string
string = "hello"
a = string[1:3]
b = string[0:6:2]
a =...
b =...

Answer 23

string = "hello there"
a = string[1:3]
b = string[0:6:2]
a = "el"
b = "hlo" (stride = 2)

Question 24

Dictionaries

Answer 24

A dictionary behaves like a list, but it can be ’indexed’ by
arbitrary variables. (Is like JSON)
D = { ’ dracula ’ : 18 , ’a ’ : 1113 , ’ mystery ’ : 6}

Question 25

Order of keys and values

Answer 25

• If items(), keys(), values(), iteritems(), iterkeys(), and itervalues() are
  called with no intervening modifications to the dictionary
  
  • then the lists will directly correspond
• This allows the creation of (value, key) pairs using zip(): pairs = zip(d.values(), d.keys())

Question 26

zip function

Answer 26

zips 2 lists together to create a list of tuple pairs of items of the same index from either list. Only as long as the shorter list.

Question 27

making dictionaries with zip() and dict()

Answer 27

zip together a list of keys and a list of values, then dict(the zip) to make it into a dictionary.

Question 28

How would you increment the value of one key? (‘dracula’)

Answer 28

D [’dracula’] += 1

Question 29

How would you add a new item to the dictionary? (‘stake’)

Answer 29

D [’stake’] = 1

Question 30

How would you check whether a key exists?

Answer 30

’ dracula ’ in D
True
»> ’ coffin ’ in D
False

Question 31

How would you remove a key-value pair?

Answer 31

Same as list but key instead of index -

D.pop(‘mystery’)

Question 32

How is hashing used in a dictionary?

Answer 32

The keys are hashed and the hash identifies each key

Question 33

When to use dictionary/list

Answer 33

Use lists when there is a natural order to the keys/indices,

but dictionaries when there is no particular order

Question 34

Immutable vs mutable

Answer 34

Immutable variables are not changed in place (memory location), while
mutable variables are changed in place

Question 35

Tuples

Answer 35

• Immutable sequences

* Automatically packed and unpacked on assignment

Question 36

when is ‘a is b’ true

Answer 36

when a and b hold the same position in memory

Question 37

a = “hello”
b = “hello”
a is b =…
a == b =…

Answer 37

a = “hello”
b = “hello”
a is b = False
a == b = True

Question 38

a = 20
b = 20
c = 500
d = 500
a is b =...
a == b =...
c is d =...
c == d =...

Answer 38

a = 20
b = 20
c = 500
d = 500
a is b = True (since 20 < 256)
a == b = True
c is d = False
c == d = True

Question 39

What is recursion?

Answer 39

When something is defined in terms of itself (calls itself from within)
Needs a base case to escape the loop when a certain condition is met. At each recursion we get closer to this case.

Question 40

What make a function a first class object?

Answer 40

A function is a first class object because you can 
• Store functions in collections
• Use functions as arguments to other functions
• Use functions as return values of other functions
• Create new functions from preexisting functions at run-time

Question 41

reduce — accumulating a result from a list

Answer 41

reduce applies the function of two arguments cumulatively to the items in the sequence S, resulting in a single value. If initial is supplied it is placed before the other items in the sequence.
- reduce(function, sequence) reduces the sequence cumulatively to a scalar result.
reduce( lambda x , y : x + y , [1 , 2 , 3 , 4 , 5])
= 15
(Computes ((((1 + 2) + 3) + 4) + 5))

Question 42

map function

Answer 42

• map(function, sequence [sequence, sequence, ...]) applies function to each item
in sequence (or sequences)

Question 43

filter function

Answer 43

• filter(function, sequence) returns the list comprising the items in sequence for which function returned True. (Same as our sieve.)

Question 44

Insertion sort

Answer 44

Build a new list from the old one inserting each element in the correct
place
Takes about N^2 operations
Useful for small lists

Question 45

Bubble sort

Answer 45

Go through the list swapping pairs of adjacent elements that are out
of order; repeat until list is sorted
On average takes about N
2 operations.
Not practical - insertion better

Question 46

Shell sort

Answer 46

• Sort pairs of elements far apart from each other.
• Progressively reduce the gap between elements to be compared.
• This can move out-of-order elements into position faster than neighbour exchange

Question 47

Merge sort

Answer 47

divide the list into rough halves, sort each half and merge the results
on average about Nlog2(N) operations
Suitable for sorting very large lists which must be stored offline
Can be implemented in-place, but complicated and not fast

Question 48

Python standard sort

Answer 48

Standard sort is list method that sorts in-place
The ‘sorted’ function returns a copy of the sorted list
> S = sorted ( L )

Question 49

Software Development Lifecycle (7 steps)

Answer 49

1) Planning - resourcing and setting up the environment
2) Requirements engineering - fleshing out the technical requirements
3) Design + prototype - does it work with test examples
4) Software development - writing production software
5) Testing - providing tests to demonstrate functionality
6) Deployment - publish and run the software in the wild
7) Operation and maintenance - upkeep

Question 50

What is a python package

Answer 50

• A Python package is just a directory containing python modules
• Python provides a module namespace within packages
 - package.module
• Python also provide 'setuptools' and 'distutils' to help configure, build
and distribute coherent package resources

Question 51

__init__.py package

Answer 51

• Necessary for package to be recognised
• Initialise any code for the package and set __all__ variables
• Often empty for basic projects